The invention relates to an apparatus and a method for detecting and varying the phase relationship in an internal combustion engine, as generically defined by the preamble to the main claim.
In an internal combustion engine, especially one with a plurality of cylinders, with a crankshaft and a camshaft, the engine control unit, as a function of the position detected for the crankshaft or camshaft, calculates when fuel is to be injected, into which cylinder, and at which instant the ignition must be tripped. It is usual to ascertain the annular position of the crankshaft with the aid of a pickup, which scans the crankshaft, or a transducer disk with a characteristic surface that is connected to the crankshaft. On the basis of the pulse train obtained, the control unit can detect the angular association.
Since the crankshaft rotates twice within one operating cycle, in the case of a four-stroke engine, however, it is not possible to determine the phase relationship of the engine unambiguously solely by scanning the crankshaft. If the phase relationship is wrong, the ignition and injection are output by the control unit with a transposition of 360xc2x0 KW. Because of the fact that one cycle of a four-stroke engine amounts to 720xc2x0 KW, and solely by means of the sensor in the transducer wheel it cannot be determined which of the four strokes is present.
If the phase signal is defective, in statistical terms every other attempt at starting will fail, since the ignition and injection are output incorrectly by the control unit by the amount of 360xc2x0 KW crankshaft. The motor accordingly fails to turn over. Furthermore, in a direct gasoline injection engine, gas from the combustion chamber is forced back into the injection valves and the fuel rail, which then impairs the starting performance even if the phase relationship is correct.
For the phase relationship to be detected correctly, the prior art typically provides a second pickup or sensor, which scans a transducer disk, communicating with the camshaft, that has a reference marking on its surface. Since the camshaft rotates only once during one work cycle, from the signal furnished by the camshaft sensor, with a single pulse per work cycle, the control unit can detect the phase relationship of the engine and perform a synchronization. Such a system is described for instance in German Patent Application P 4230616.7.
German Patent Disclosure DE-OS 4418578 discloses an apparatus for detecting the phase relationship in an internal combustion engine that makes do without a second sensor in the form of a camshaft sensor, by performing a check of the phase relationship under certain conditions; this condition is advantageously the resumption of sequential fuel injection after the overrunning shutoff. More precisely, by way of a segment time comparison, it is ascertained here whether the rpm of individual injected cylinders occurs in the expected annular position, and from this the conclusion of a correct or incorrect phase relationship is drawn; the term xe2x80x9csegment timexe2x80x9d means a time that elapses while the crankshaft rotates by an angle that is generally designated as a segment.
In direct gasoline injection engines with one fuel injection valve per piston of an internal combustion engine, the emergency operation concept of intake tube injection with dual ignition cannot be employed. Furthermore, if the phase relationship is wrong, gas is forced out of the combustion chamber back into the injection valves and the fuel rail, which means that even if the phase relationship is correct, the starting performance is impaired, or starting is prevented entirely.
The present invention therefore has the object of disclosing an apparatus and a method by which detection of the phase relationship is possible at starting, and by which an improved starting performance in the event of failure of the phase signal is obtained. According to the invention, this object is attained by the body of the main claim and by the dependent claims.
The apparatus according to the invention has the a substantial advantage that already existing component groups and components can be used; no additional camshaft sensor is required, and no extra pressure sensors are necessary, either. The rail pressure evaluation is typically done directly in the control unit, without additional circuitry. Optionally, the pressure signal of the fuel rail signal can also be delivered to the control unit for evaluation by way of a simple analog/digital comparator circuit.
After detection of the reference marking, a special injection without ignition takes place in one of the fuel injection valves at top dead center.
If the phase relationship is wrong at the time of engine starting, the affected injection valve into which blowback occurs from the compression counterpressure is immediately closed, and the pressure increase is imparted to the control unit, for instance via the analog/digital comparator circuit. A reverse synchronization of the injection and ignition by 360xc2x0 KW is thereupon tripped by the control unit.